The move appears to be another contract dispute after the online retailer began a protracted spat with publisher Hachette Book Group this year.

Physical copies of titles such as "Maleficent" and "Captain America: The Winter Soldier" were unavailable for order onAmazon.com last night.

Digital copies of some of the movies in question were still available for pre-order.

Amazon has been waging a battle against Hachette, the fourth-largest US book publisher, over the price the online retailer can charge for e-books. Hachette is owned by France's Lagardere.

A group called Authors United ran a two-page ad in the New York Times on Sunday, criticising Amazon for halting pre-orders from some Hachette authors and slowing delivery of books by Hachette authors.

The ad was signed by more than 900 writers, including Stephen King and Donna Tartt.

In response, Amazon.com's Books Team ran a message on a website reiterating its arguments for cheaper ebooks, and suggested people email Hachette CEO Michael Pietsch. The company published Pietsch's email address and listed key points people might want to make.

Pietsch replied to every individual who emailed him saying that the dispute started because Amazon is seeking a lot more profit and even more market share at the expense of authors, bookstores and Hachette.

"Both Hachette and Amazon are big businesses and neither should claim a monopoly on enlightenment, but we do believe in a book industry where talent is respected and choice continues to be offered to the reading public," Pietsch wrote on Sunday, a copy of which was emailed to Reuters.

"Once again, we call on Amazon to withdraw the sanctionsa gainst Hachette's authors that they have unilaterally imposed, and restore their books to normal levels of availability," he added.

Amazon says pricing e-books at $14.99 or $19.99 is too expensive. It argues that cheaper e-books sell more copies and so ultimately generate more revenue and more royalties for authors.